Acids-Bases Reactions

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• Acids-Bases Reactions

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Acids Bases

• What causes acid rain? And how can we prevent the
  damage?
• Why do Perrier drinking chickens give better eggs
  than chickens who drink regular water?
• These are the types of questions we will be able
  to answer after this unit.

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First Proposed Theory

• Arrhenius Theory of Acids Bases
• An acid is any substance which releases H(aq) in
  water
• - it is any ionic species that start with H
  
• - it tastes sour, turns blue litmus paper red
• eg. HCl, HNO3, H2SO4
• A base is any substance which releases OH-(aq) in
  water
• - it is any ionic species that ends with OH
• - it tastes bitter, feels slippery, turns red
  litmus paper blue
• eg. NaOH, KOH, Ca(OH)2

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• A sAlt results from the neutralization rxn. of an
  acid base
• Neutralization rxn
• Acid Base ? salt H2O
• Net Ionic Equation
• H OH- ? H2O
• Eg. HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l)

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Q Predict the products balance the following
Neutralization Reactions

• H2SO4(aq) NaOH(aq) ?
• H2SO4(aq) 2 NaOH(aq) ? Na2SO4(aq) 2
  H2O(l)
• H3PO4(aq) KOH(aq) ?
• H3PO4(aq) 3 KOH(aq) ? K3PO4(aq) 3 H2O(l)
• H4P2O7(aq) NaOH(aq) ?
• H4P2O7(aq) 4 NaOH(aq) ? Na4P2O7(aq) 4
  H2O(l)

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Second Proposed Theory

• Bronsted-Lowry Theory of Acids Bases
• more general includes equilibrium rxns
• An acid is a substance that DONATES a PROTON (H)
• An base is a substance that Accepts a PROTON (H)
• Eg. NH3 H2O ? NH4 OH-
• NH3 gained a proton ? NH4
• Thus, NH3 BASE
• H2O lost a proton ? OH-
• Thus, H2O ACID

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Your Turn!

• CH3COOH H2O ? CH3COO- H3O
• (lost/donated H) (gained H)
• ACID BASE
• Which reactants acts as an acid which as a
  base?
• HNO3 H2O ? NO3- H3O
• HCO3- SO32- ? CO32- HSO3-
• HS- H2PO4- ? H2S HPO42-
• H3PO4 CH3COO- ? H2PO4- CH3COOH
• CO32- HF ? HCO3- F-

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Classifying Acids

• A monoprotic acid can donate 1 proton.
• A DIprotic acid can donate up to 2 proton.
• A triprotic acid can donate up to 3 proton.
• All acids that can donate more than 1 proton are
  known as polyprotic acids.

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Amphiprotic Substances

• Amphiprotic substances can act as an acid or a
  base.
• eg. Water
• NH3 H2O ? NH4 OH-
• Base acid
• CH3COOH H2O ? CH3COO- H3O
• Acid base

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• Apart from water, amphiprotic substances start
  with H and have a (?) charge.
• eg. H2PO4- , HS-, HCO3-
• Base acid
• H3PO4 ? H2PO4- ? HPO42-
• Accepts H Donates H

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• NOTE In every Bronsted-Lowry rxn. there is an
  acid and a base on both sides of the eqn.
• CH3COOH H2O ? CH3COO- H3O
• acid base base
  acid

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Q Which do you think exhibit amphiprotic
behavior?

• Se2-
• HSe-
• H2Se
• H3PO4
• HPO42-
• HSO3-

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Q Identify each species as an acid or base.

1. HF SO32- ? F- HSO3-
2. H2O HCO3- ? H3O CO32-
3. NO2- H2O ? OH- HNO2
4. H2PO- S2- ? HS- HPO42-
5. N2H5 SO42- ? N2H4 HSO4-

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Conjugate Acid Bases

• A conjugate acid-base pair is a pair of
  chemical species that only differ by ONE proton.
• Eg. NH4 H2O ? NH3 H3O
• Acid has the extra proton (ability to donate
  it)

Conjugate Pair Conjugate Acid Conjugate Base
NH4 , NH3 NH4 NH3
H2O, H3O H3O H2O
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Assignment

• Acid Base Handout
• ? Questions 1 ? 4

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Buffer Solutions

• Buffers are solutions with the ability to resist
  the addition of strong acids or strong bases,
  within limits.
• eg. CH3COOH and its salt NaCH3COO
• Most buffer solutions are made up using a WEAK
  ACID and its sodium salt!

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When a strong base such as NaOH is added to the
buffer CH3COOH

• CH3COOH reacts with and consumes the excess OH-
  
• OH- reacts with the H3O ion from the acid in
  the following reaction
• H2O CH3COOH  lt---gt  H3O CH3COO-
• H3O OH- lt--------gt H2O  

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When a strong acid such as HCl is added to the
buffer CH3COOH

• H3O reacts with the CH3COOH- ions of the salt
  and form more undissociated CH3COOH
• H3O CH3COO- lt-------gt H2O CH3COOH
• There is a limit to the quantity of H or OH-
  that a buffer can absorb without undergoing a
  significant change in pH.

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Buffer Components

• A buffer has two components.
• HA        NaA ---gt Na A-
• (weak acid) (a soluble salt of the weak
  acid)
• Therefore any extra H3O will be neutralized by
  the A- in the buffer
• H3O A-    lt-------gt  HA H2O
• And any extra OH- that is added will be
  neutralized by the acid
•     HA OH-   lt------gt  A- H2O

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Sample Problem

• CH3COOH H2O ? CH3COO? H3O
• 1.0 M 1.0M
• Original Ratio Acid 1.0 1.0
• Base 1.0
• New Ratio 1.1 1.22
• 0.9

Add 0.1 mol H3O
ACID
1.1
BASE
0.9
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Using Ka

• Original
• H3O (1.8 x 10-5)(1.0)
• 1.8 x 10-5
• pH 4.74
• After
• H3O (1.8 x 10-5)(1.22)
• 2.5 x 10-5
• pH 4.66
• pH change of 0.08

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With no buffer present

• Adding 0.1 mol of acid to H2O would change the pH
  by 6.00!
• pH water 7
• pH water with 0.1M H3O 1
• Thus a difference of 6.